1. Field
This technology relates generally to routing protocol and, more particularly, to routing protocol for computer networks.
2. Background Art
In computer communication theory relating to packet-switched networks, a distance-vector routing protocol is one of the two major classes of routing protocols, the other major class being the link-state protocol. Distance-vector routing protocols use the Bellman-Ford algorithm, Ford-Fulkerson algorithm to calculate paths. A distance-vector routing protocol requires that a router informs its neighbours of topology changes periodically. Compared to link-state protocols, which require a router to inform all the nodes in a network of topology changes, distance-vector routing protocols have less computational complexity and message overhead. The term distance vector refers to the fact that the protocol manipulates vectors (arrays) of distances to other nodes in the network. Examples of distance-vector routing protocols include RIPv1 and RIPv2 and IGRP. Distance-vector protocols are based on calculating the direction and distance to any link in a network. “Direction” usually means the next hop address and the exit interface. “Distance” is a measure of the cost to reach a certain node. The least cost route between any two nodes is the route with minimum distance. Each node maintains a vector (table) of minimum distance to every node. The cost of reaching a destination is calculated using various route metrics. RIP uses the hop count of the destination whereas IGRP takes into account other information such as node delay and available bandwidth. Updates are performed periodically in a distance-vector protocol where all or part of a router's routing table is sent to all its neighbors that are configured to use the same distance-vector routing protocol. Once a router has this information it is able to amend its own routing table to reflect the changes and then inform its neighbors of the changes. This process has been described as ‘routing by rumor’ because routers are relying on the information they receive from other routers and cannot determine if the information is actually valid and true. There are a number of features which can be used to help with instability and inaccurate routing information.
Distance Vector protocols view networks in terms of adjacent routers and hop counts, which also happens to be the metric used. The “hop” count (max of 15 for RIP, 16 is deemed unreachable and 255 for IGMP), will increase by one every time the packet transits through a router. So the router makes decisions about the way a packet will travel, based on the amount of hops it takes to reach the destination and if it had 2 different ways to get there, it will simply send it via the shortest path, regardless of the connection speed.
Multicast protocols in computer networks often use information from routers in a network using Distance Vector Routing (DVR) and often run a data propagation mechanism known as Reverse Path Forwarding (RPF) using the DVR information. Multicasting in computer networks means communication among a group of users where formation of the group is based on the particular interest of its members. Some examples are: Video conferencing, social networking, distance learning, communication in battle field, etc. At any given time thousands of such communications are transmitted on networks. One of the most widely used multicast protocols is known as Distance Vector Multicast Routing Protocol (DVMRP), which uses the DVR information from the routers.
For its proper implementation, it generates a very large number of control packets, known as prune packets; these prune packets consume a considerable amount of network bandwidth, which results in slower traffic movement in the networks causing delay in communication. Since transmissions of these packets have to be done by routers, it keeps routers so busy that other communications (i.e., other than multicasting) such as email, file transfer, web browsing etc. which need these routers are affected and get delayed. It may also affect the speed at which an urgent multicast session must complete. In reality thousands of multicasting sessions take place at any given time and therefore in general the overall traffic-load situation is extremely bad from the viewpoint of communication delay and congestion when DVMRP is used.
While this protocol is not hard to implement, much improvement is needed from the viewpoint of more effective use of the network bandwidth by drastically reducing the number of prune packets generated. As pointed out above more effective bandwidth utilization means enhancements of the data communication speed as well as less probable occurrence of congestion in a network. It can therefore make a network more cost-effective.